It is becoming increasingly common to eliminate the traditional direct link, (usually a mechanical linkage such as a "Bowden" cable), between the driver operated accelerator pedal of a motor vehicle and the fuelling system of its engine. It is replaced with electrical control of the engine fuelling, normally in the form of an engine management system running closed loop feed-back control. Such systems are commonly known in the art as "drive by wire".
"Drive by wire" systems usually employ a pedal demand potentiometer connected to the driver operated accelerator pedal to provide a signal of demanded power to the engine management system. The engine management system controls the supply of fuel and air to the engine in response to that pedal demand signal.
When a vehicle is to be used off-road, in conditions where the surface over which it is travelling is rough or uneven, there is a requirement for a low sensitivity in the accelerator pedal, at least over the initial range of pedal travel. This is because there is generally a lot of vibration which makes the vehicle hard to control if the accelerator is too sensitive. On the other hand, for on-road driving, where the driving surface is relatively smooth, a more sensitive accelerator pedal is usually preferable to give a more powerful feel to the vehicle. Known systems generally result in a compromise between these conflicting requirements.
EP 0 322 790 discloses a slip control system in which various throttle characteristics are available which limit the power available to varying degrees. The control system changes between characteristics to reduce power if slip is detected.
GB 2154763 and FR 2483012 each disclose a system having different throttle characteristics which are selectable by the driver to give the driving characteristics required, such a sporty feel or economy of fuel.
U.S. Pat. No. 5,111,570 discloses a throttle regulated traction control system which varies the response of the throttle so as to match the slip rate of the drive wheels with a target slip rate. The object of U.S. Pat. No. 5,111,570 is to prevent a loss of speed when driving on rough roads which might result from an erroneously high determination of the slip rate and subsequently undue decrease in the driving force available.
The problem outlined above has not been addressed by the prior art.